KIRK: That should make a good specimen.
SULU: (holding pink animal with a horn) Temperature's starting to drop.
KIRK: Yeah. At night it gets down to a hundred and twenty degrees below zero.
SULU: That's nippy. 
FISHER: Hey!
KIRK: What happened?
FISHER: I fell off that bank, sir. Cut my hand.
KIRK: Let's see it. Get back to the ship. Report to the Sickbay.
FISHER: Yes, sir. Geological Technician Fisher. Ready to beam up.

[Transporter room]

SCOTT: Right. Locked onto you. Energise. Coadjutor engagement.
WILSON: What happened?
FISHER: I took a flop.
WILSON: Onto what?
FISHER: I don't know. Some kind of yellow ore.
SCOTT: Magnetic. Decontaminate that uniform.
FISHER: Yes, sir. (;eaves)
SCOTT: That acted like a burnout.
KIRK [OC]: Captain Kirk ready to beam up.
SCOTT: Just one moment, Captain. It checks out okay now. You better go get a synchronic meter so we can double-check.
WILSON: Yes sir.
SCOTT: All right, Captain. Locked onto you. (Kirk stumbles as he leaves the platform) Are you all right, Captain?
KIRK: Yes, I'm all right. Just a little dizzy.
SCOTT: Let me give you a hand.
KIRK: I can't get through there. Nothing serious. Don't leave the transporter room unattended.
SCOTT: Wilson will be right back, sir.
(both leave, and another Kirk materialises on the pad)

Captain's Log, stardate 1672.1. Specimen-gathering mission on planet Alpha 177. Unknown to any of us during this time, a duplicate of me, some strange alter ego, had been created by the transporter malfunction.

[Transporter room]

WILSON: Captain? Are you all right, sir? Can I give you a hand, sir? Captain?

[Corridor]

UHURA [OC]: Bridge to all decks. Section duty officers, check communication lines.
KIRK: Thank you.
SCOTT: It might profit you to let Doctor McCoy give you the once-over.
KIRK: All right, Engineer, I'll have my engines looked to.

[Kirk's quarters]

RAND: Ship's manifests, sir. I think they're in order now.
KIRK: Thank you, Yeoman.
RAND: I've checked
KIRK: That's all.
RAND: Yes, sir. (leaves Kirk to lie down on bed)

[Sickbay]

MCCOY: You picked a good day, Fisher. Business has been lousy. What'd you do, take a fall on purpose so you could get a little vacation?
KIRK: Saurian brandy.
Back to duty status, Fisher. I have no sympathy for clumsiness.
FISHER: No, sir. The hand's much better, sir. (leaves)
MCCOY: What can I do for you, Jim?
KIRK: (grabbing him by the neck) I said, give me the brandy! (leaves with bottle and goes to Rand's quarters)

[Kirk's quarters]

KIRK: Yeah.
SPOCK [OC]: Mister Spock.
KIRK: Come in. Yes, Mister Spock, what is it?
SPOCK: Is there something I can do for you, Captain?
KIRK: Like what?
SPOCK: Well, Doctor McCoy seemed to think I should check on you.
KIRK: That's nice. Come on, Spock, I know that look. What is it?
SPOCK: Well, our good doctor said that you were acting like a wild man, demanded brandy.
KIRK: Our good doctor's been putting you on again.
SPOCK: Hmm. Well, in that case, if you'll excuse the intrusion Captain, I'll get back to my work.
KIRK: I'll tell him you were properly annoyed.
SPOCK: Captain.

[Transporter room]

KIRK: What is it, Scotty?
SCOTT: Transporter breakdown. Continue circuit testing. We beamed up this animal and, well, look for yourself. It's in this specimen case. (opens lid to reveal angry pink animal)
KIRK: Yes?
SCOTT: A few seconds after they sent this one up through the transporter, that duplicate appeared. Except it's not a duplicate, it's an opposite. Two of the same animal, but different. One gentle, this. One mean and fierce, that. Some kind of savage, ferocious opposite. Captain, we don't dare send Mister Sulu and the landing party up. If this should happen to a man.
KIRK: Oh, my.

[Rand's quarters]

RAND: Oh! Captain, you startled me. Is there something that you? Can I help you, Captain?
KIRK: Jim will do here, Janice.
RAND: Oh.
KIRK: You're too beautiful to ignore. Too much woman. We've both been pretending too long. (grabs her) Stop pretending. Let's stop pretending. Come here, Janice. Don't fight me. Don't fight me, Janice. (kisses her)
RAND: Captain!
KIRK: Just a minute, Janice. Just a minute! (forces her onto the floor, she scratches his face and gets away to the door which opens just as Fisher is passing by)
RAND: Call Mister Spock! Call Mister Spock!

[Corridor]

FISHER: Geological Technician Fisher. Deck twelve, section (Kirk grabs him and hits him, hard)

[Kirk's quarters]

KIRK: Me? My yeoman said that? I've been resting here since you left me. Alone, Mister Spock.
SPOCK: Doctor McCoy reports that you demanded this brandy in Sickbay and left with it. I found this bottle in Yeoman Rand's quarters.
KIRK: Not true. I haven't been to the Sickbay. Let's find out what's going on.

[Turbolift]

KIRK: Sickbay. (just missing the other Kirk nursing grazed knuckles, who goes into his quarters)

[Sickbay]

RAND: Then he kissed me and he said that we, that he was the Captain and he could order me. I didn't know what to do. When you mentioned the feelings we'd been hiding, and you started talking about us.
KIRK: Us?
RAND: Well, he is the captain. I couldn't just. You started hurting me. I had to fight you, and scratch your face.
KIRK: Yeoman, look at me. Look at me, look at my face. Are there any scratches?
RAND: I was sure I scratched you. I was frightened. Maybe
KIRK: Yeoman. I was in my room. It wasn't me.
RAND: Sir, Fisher saw you, too.
KIRK: Fisher saw?
RAND: If it hadn't been. I can understand. I don't want to get you into trouble. I wouldn't have even mentioned it!
KIRK: It wasn't me!
FISHER: It was you, sir.
KIRK: Do you know what you're saying?
FISHER: Yes, I know what I'm saying.
MCCOY: Back to that bed, bucko. Come on, let's go.
SPOCK: You can go now, Yeoman. (Rand leaves) There's only one logical answer. We have an impostor aboard.

Captain's Log, stardate 1672.9. On the planet's surface, temperatures are beginning to drop, our landing party there in growing jeopardy. Due to the malfunction of the ship's transporter, an unexplained duplicate of myself definitely exists.

[Transporter room]

KIRK: How did all this happen?
SCOTT: I don't know sir, but when Fisher came up, his suit was covered with a soft yellow ore that had highly unusual properties. It may have caused an overload. Can't tell, not yet.
KIRK: Does the transporter work at all?
SCOTT: Yes sir, but we don't dare bring up the landing party. It might be duplicated like this animal.
KIRK: How long will it take you to find the trouble?
SCOTT: Can't say, sir.
KIRK: We just can't leave those four men down there. It's getting dark. They'll die. The surface temperature of that planet goes down to a hundred and twenty degrees below zero at night.
SCOTT: We're doing everything we can, sir.
KIRK: Yes, I know, Scotty.
SPOCK: About your double, Captain.
KIRK: Yes, er, yes, we'll have to find him. Search parties, Mister Spock. Organise search parties.
SPOCK: We can't take a chance on killing it. We have no previous experience, no way of knowing what would happen to you.
KIRK: Yes, that's right. We don't know, but the men have to be armed. The men are to be armed, with their phasers locked, I repeat, locked, on setting number one. There can't be any chance of him being killed. He's to be taken without. If the men are forced to fire, he can't be killed.
SPOCK: How shall we explain it to them, Captain? The search parties are to capture you?
KIRK: Tell them.
SPOCK: The search parties, Captain.
KIRK: Yes, I'll make an announcement to the entire crew, tell them what happened. It's a good crew. They deserve to know.
SPOCK: Captain, no disrespect intended, but you must surely realise you can't announce the full truth to the crew. You're the Captain of this ship. You haven't the right to be vulnerable in the eyes of the crew. You can't afford the luxury of being anything less than perfect. If you do, they lose faith, and you lose command.
KIRK: Yes, I do know that, Mister Spock. What I don't know is why I forgot that just now. Mister Spock, if you see me slipping again, your orders, your orders are to tell me.
SPOCK: Understood, Captain.

Captain's Log, stardate 1673.1. Something has happened to me. Somehow, in being duplicated, I have lost my strength of will. Decisions are becoming more and more difficult.

[Kirk's quarters]

KIRK [OC]: This is the Captain speaking. There's an impostor aboard the ship, a man who looks exactly like me and is pretending to be me. This man is dangerous. Utmost caution is to be observed. All crew members are to arm themselves. The impostor may be identified by scratches on his face. Repeat, the impostor may be identified by scratches on his face.

[Bridge]

KIRK: Section chiefs, assign personnel to the search. All search parties

[Kirk's quarters]

KIRK [OC]: report to Mister Spock for assignment.

[Bridge]

KIRK: Something?
SPOCK: About the phaser weapons to be set for stunning force and locked.
KIRK: Oh, yes, yes. All hand phasers must be set on base cycle, stunning force.

[Kirk's quarters]

KIRK [OC]: The impostor is not to be injured. Use minimum force. Repeat, the imposter
KIRK: I'm Captain Kirk!
KIRK [OC]: Is not to be injured.
KIRK: I'm Captain Kirk. I'm Captain Kirk! I'm Captain Kirk! I'm Captain Kirk! (goes to mirror, covers scratches with makeup, opens door) Wilson!
WILSON: Sir?
KIRK: Wilson, give me your phaser.
WILSON: Yes, sir.
KIRK: How have you been?
WILSON: Fine, sir. (Kirk grabs and hits him)

[Planet surface]

KIRK [OC]: How's it going down there, Mister Sulu?
SULU: It's already twenty degrees below zero. Can't exactly

[Briefing room]

SULU [OC]: call it balmy.
KIRK: Isn't there any way we can help them?
SPOCK: Thermal heaters were transported down. They duplicated. They won't operate.
KIRK: Then we've got to get those men up.
CREWMAN [OC]: Mister Spock?
SPOCK: Spock here.
CREWMAN [OC]: Transporter Technician Wilson found injured near the Captain's cabin. He says the impostor attacked him, called him by name, took his hand phaser.
SPOCK: Acknowledged. Continue the search.
KIRK: We've got to find him before he, but how?
SPOCK: Apparently, this double, however different in temperament, has your knowledge of the ship, its crew, its devices. This being the case, perhaps we can outguess him by determining his next move. Knowing how the ship is laid out, where would you go to elude a mass search?
KIRK: The lower levels. The Engineering deck.

[Engineering]

SPOCK: Set and locked on base cycle to stun, not to kill. What about your phaser, Captain? Don't you think we ought to get some help, Captain?
KIRK: No. I don't want anyone else to see the
SPOCK: Captain, you ordered me to tell you.
KIRK: Mister Spock, if I'm to be the Captain, I've got to act like one.
(they split up to search, and Kirk comes face to face with himself)
KIRK: You can't hurt me. You can't kill me. You can't. Don't you understand? I'm part of you. You need me. I need you.
OTHER KIRK: I don't need you. (Spock neck-pinches him, and his phaser fire hits a panel instead)

[Sickbay]

MCCOY: He'll be regaining consciousness soon, and not knowing what his physical state is, I don't think I dare give him a tranquilizer of any kind. I think we'd better bind him.
KIRK: Yes. yes, all right. What's the matter with me?
SPOCK: Judging from my observations, Captain, you're rapidly losing the power of decision.
MCCOY: You have a point, Spock?
SPOCK: Yes, always, Doctor. We have here an unusual opportunity to appraise the human mind, or to examine, in Earth terms, the roles of good and evil in a man. His negative side, which you call hostility, lust, violence, and his positive side, which Earth people express as compassion, love, tenderness.
MCCOY: It's the Captain's guts you're analysing. Are you of that, Spock?
SPOCK: Yes, and what is it that makes one man an exceptional leader? We see indications that it's his negative side which makes him strong, that his evil side, if you will, properly controlled and disciplined, is vital to his strength. Your negative side removed from you, the power of command begins to elude you.
KIRK: What is your point, Mister Spock?
SPOCK: If your power of command continues to weaken, you'll soon be unable to function as Captain. You must be prepared for that.
MCCOY: You have your intellect, Jim. You can fight with that!
KIRK: For how long?
SPOCK: If I seem insensitive to what you're going through, Captain, understand it's the way I am.
SCOTT [OC]: Captain Kirk.
KIRK: Kirk here.
SCOTT [OC]: Mister Scott, sir, on the lower level of the Engineering deck.

[Engineering]

SCOTT: I've found a new trouble with the transporter. The casing has a wide gap ripped in it. (the phaser damage) The main circuits

[Sickbay]

SCOTT [OC]: have been burned through. The abort control circuit is gone altogether.

[Planet surface]

SULU: Can you give us a status report, Captain? Temperature's still dropping. Now forty one degrees below zero.
KIRK [OC]: We've located the trouble. It shouldn't be much longer.
SULU: Do you think you might be able to find a long rope somewhere and lower us down a pot of hot coffee?

[Sickbay]

KIRK: I'll see what we can do.
SULU [OC]: Rice wine will do, if you're short on coffee.
KIRK: Engineering deck, Kirk here.
SCOTT [OC]: Scott here, Captain.
KIRK: That unit, Scotty, status report.
SCOTT [OC]: The transporter unit ioniser. Nothing much left of it, sir.
KIRK: How bad is it?
SCOTT [OC]: We can't repair it in less than a week.

Captain's Log, stardate 1673.5. Transporter still inoperable. My negative self is under restraint in Sickbay. My own indecisiveness growing. My force of will steadily weakening. On the planet, condition critical. Surface temperature is seventy five degrees below zero, still dropping.

[Planet surface]

SULU: (using phaser to heat rocks) I think we ought to give room service another call. That coffee's taking too long. Enterprise, this is Sulu.

[Briefing room]

KIRK: Kirk here, Mister Sulu.
SULU [OC]: Hot line direct to the Captain. Are we that far gone?
KIRK: I gave everybody the afternoon off. I'm watching the store.

[Planet surface]

KIRK [OC]: How is it down there?
SULU: Oh, lovely, except that the frost is building up. We're using hand phasers to heat the rocks. One phaser quit on us, three still operating. Any possibility of getting us back aboard before the skiing season opens down here?

[Briefing room]

SPOCK: This is Spock, Mister Sulu. You'll have to hold on a little longer. There's no other way. Survival procedures, Mister Sulu.
SULU [OC]: Per your training programme, Mister Spock.

[Sickbay]

(other Kirk is screaming)
KIRK: What happened?
MCCOY: Apparently the body functioning weakened during the duplication process. A fact I failed to consider.
KIRK: He's not dying?
KIRK: Yes, he is.
OTHER KIRK: Help me.
KIRK: How can he die? Can I survive without him?
MCCOY: I don't know, Jim.
KIRK: Don't be afraid. Here's my hand. Hold on. You don't have to be afraid. I won't let go. Hold on. You won't be afraid if you use your mind and think! Think! You can do it. That's it!
MCCOY: Jim, he is back! Jim, you can use that brandy now. In fact, I'll join you.
KIRK: I have to take him back inside myself. I can't survive without him. I don't want him back. He's like an animal, a thoughtless, brutal animal, and yet it's me. Me.
MCCOY: Jim, you're no different than anyone else. We all have our darker side. We need it! It's half of what we are. It's not really ugly, it's human.
KIRK: Human.
MCCOY: Yes, human. A lot of what he is makes you the man you are. God forbid I should have to agree with Spock, but he was right. Without the negative side, you wouldn't be the Captain. You couldn't be, and you know it. Your strength of command lies mostly in him.
KIRK: What do I have?
MCCOY: You have the goodness.
KIRK: Not enough. I have a ship to command.
MCCOY: The intelligence, the logic. It appears your half has most of that, and perhaps that's where man's essential courage comes from. For you see, he was afraid and you weren't.
SPOCK [OC]: Captain Kirk.
KIRK: Kirk here.
SPOCK [OC]: Spock here. Would you come to the transporter room. We think we may have found an answer.
KIRK: Coming.

[Transporter room]

KIRK: What is it?
SCOTT: We've found a way to get the transporter working, sir.
SPOCK: We've attached some bypass and leader circuits to compensate for the difference. Tied directly into the impulse engines, there shouldn't be more than a five point variation in the velocity balance. I suggest we send the animal through. Captain.
KIRK: Yes, yes. Go ahead.
SCOTT: (opening box with angry animal in it) I'll grab him by the scruff of the neck and hold him as long as I can.
KIRK: Don't hurt him.
SPOCK: It's painless and quick. The animal will be unconscious for only a few minutes. (sedates it)
SCOTT: If this doesn't work, I don't know what will.
SPOCK: Energise. Reverse.
SPOCK: The shock of putting him back together seems to have been too much for him.
MCCOY: He's dead, Jim.

Captain's Log, stardate 1673.1. Entry made by Second Officer Spock. Captain Kirk retains command of this vessel, but his force of will rapidly fading. Condition of landing party critical. Transporter unit still under repair.

[Sickbay]

MCCOY: Autopsy in-depth. Hurry. I don't know. Animal could have died of some kind of shock.
SPOCK: For once, I agree with you.
MCCOY: I said could have, Mister Spock. We won't know until we get a full post-mortem.
SPOCK: No autopsy is necessary to know that the animal was terrified, confused. It was split into two halves and suddenly thrust back together again. Thus shock induced by blind terror.
KIRK: Yes, yes, that sounds likely.
SPOCK: It couldn't understand. You can. You have your intelligence controlling your fear.
KIRK: Get the transporter room ready.
MCCOY: Could be, if, maybe. All guesswork so far. Just theory. Jim, why don't you give me a chance to do an autopsy and let Spock check the transporter circuits again.
KIRK: That sounds, sounds reasonable. We should double-check everything.
SPOCK: Aren't you forgetting something, Captain?
KIRK: No, I don't think I've for
SPOCK: Your men on the planet surface. How much time do they have left?
KIRK: Yes, that's right. The men. We have to take the chance, Bones. Their lives
MCCOY: Suppose it wasn't shock, Jim. Suppose death was caused by transporter malfunction. Then you'd die. They'd die, anyway. Jim, you can't risk your life on a theory!
SPOCK: Being split in two halves is no theory with me, Doctor. I have a human half, you see, as well as an alien half, submerged, constantly at war with each other. Personal experience, Doctor. I survive it because my intelligence wins over both, makes them live together. Your intelligence would enable you to survive as well.
KIRK: Help me. Somebody make the decision.
SPOCK: Are you relinquishing your command, Captain?
KIRK: No. No, I'm not.
MCCOY: Well then, we can't help you, Jim. The decision is yours.
KIRK: Mister Spock, ready the transporter room. Bones, continue the autopsy.
UHURA [OC]: Captain Kirk, I have a tie-in with Sulu now.
KIRK: Kirk here.

[Planet surface]

SULU: Captain K-Kirk, Sulu here. One hundred seventeen below. Can't last much longer.

[Sickbay]

SULU [OC]: Can't see clearly, Doctor, to read top indicator. Think the cold penetrating communicator. Two men unconscious. No time. No. Can't wait. No time.
KIRK: Mister Sulu. Mister Sulu. Can't wait. Can't let them die.
OTHER KIRK: What are you going to do?
KIRK: Go through the transporter, both of us.
OTHER KIRK: There's nothing I can do to stop you.
KIRK: It's what I have to do. It's what I have to do. What we have to do.
OTHER KIRK: I won't fight you anymore. Oh, I feel so weak. I'll be glad when this is over. (grabs Kirk and knocks him out)

[Corridor]

KIRK: Janice, hello.
RAND: Captain, I
KIRK: Yeoman, I owe you an explanation.
RAND: No.
KIRK: Yes, I do. The transporter malfunctioned, divided me, created a duplicate. The animal part of me came to your cabin. He even scratched me to make us look more alike. I'd like the chance to explain it to you. You don't mind if I come to your cabin later?
RAND: No, sir.
KIRK: (enters turbolift) Bridge.

[Bridge]

FARRELL: No word from Mister Sulu, sir.
OTHER KIRK: Prepare to leave orbit, Mister Farrell. Well?
FARRELL: Captain!
OTHER KIRK: I gave you an order, Mister Farrell.
FARRELL: But what about
OTHER KIRK: They can't be saved. Prepare to leave orbit.
FARRELL: Yes, sir.
SPOCK: Captain, I thought the plan
OTHER KIRK: I've changed my mind. Man your station, Mister Spock. (McCoy enters with another Kirk, identically dressed) Grab him. He's the impostor.
MCCOY: No!
OTHER KIRK: McCoy, he's fooled you.
MCCOY: He (the one in the captain's chair) attacked him.
OTHER KIRK: Mister Spock, you know who I am. You know what that is.
FARRELL: Mister Spock, which one? What do we do?
SPOCK: We'll let the captain handle this.
OTHER KIRK: I'm the captain. Isn't that obvious? Look at his face. Remember the scratches? Look how he's tried to hide them. He wants you to think that he's Captain Kirk. You know who I am.
KIRK: Yes, I know.
OTHER KIRK: You want to kill me, don't you? Farrell, James, grab him. He'll destroy the ship! I'm the Captain. Don't you understand? I'm captain of the ship! (starts attacking the crew) I'm the captain! This is my ship! My ship! It's mine! I'll kill you.
KIRK: Can half a man live?
OTHER KIRK: Take another step, you'll die.
KIRK: Then we'll both die.
OTHER KIRK: Please, I don't want to. Don't make me. Don't make me. (Kirk takes phaser off him) I don't want to go back. Please! I want to live!
KIRK: You will. Both of us.
OTHER KIRK: I want to live!

[Transporter room]

SPOCK: You'll have to hold on to him, Captain.
KIRK: Mister Spock.
SPOCK: Captain?
KIRK: If this doesn't work.
SPOCK: Understood, Captain.
KIRK: Mister Spock.
SPOCK: Ready. (beams them out)
MCCOY: Well, Mister Spock? (one figure is beamed back) Jim?
KIRK: Get those men aboard fast.
SPOCK: Right away, Captain.
MCCOY: (as the party is wheeled away) Severe exposure and frostbite, but I think they'll make it. How do you feel, Jim?
KIRK: How? I've seen a part of myself no man should ever see.

[Bridge]

FARRELL: Status report, green.
SPOCK: All sections report ready, sir.
KIRK: Good. Thank you, Mister Spock, from both of us.
SPOCK: Shall I pass that on to the crew, sir?
KIRK: The impostor's back where he belongs. Let's forget him.
RAND: Captain? The impostor told me what happened, who he really was, and I'd just like to say that. Well, sir, what I'd like is
KIRK: Thank you, Yeoman.
SPOCK: The, er, impostor had some interesting qualities, wouldn't you say, Yeoman?
KIRK: This is the Captain speaking. Navigator, set in course correction. Helmsman, steady as she goes.